Radio receiver



Dec. 8, 1936. R, A BRADEN 2,063,295

RADIO REGElVEYR Filed Dec. 1, `1955 2 Sheets-Sheer?I l 9.0,. O ...AMO

R. A. BRADEN RADIO RECEIVER Dec. 8, 1936.

Filed Deo. l, 1955 2 Sheets-Sheet www EN www www fufrvg INvENToR: Rene f1. Braden,

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Patented Dec. 8, 1936 UNITED STATES PATE-NT OFFICE RADro RECEIVER Delaware Application December 1, 1933, Serial No. 700,472

9 Claims.

My invention relates to radio receivers and particularly to circuits and apparatus for providing an improved tuning control therefor.

An objectionable feature of present high quality radio receivers is that the selectivity has been increased to a point Where they are somewhat diilcult to tune. Furthermore, it is feasible, and desirable from many standpoints, to make the tuning of radio receivers still sharper, one way of accomplishing this being to utilize a sharply selective background noise suppressor circuit. It is impractical to do this, however, when employing the usual tuning control for the reason that such a receiver must be tuned very carefully in order to avoid tuning through the desired station.

lt is, accordingly, an object of my invention to provide an improved tuning device for radio receivers.

More specifically, it is an object of my invention to provide automatic tuning control means which overcomes the above-mentioned objection to sharply tuned receivers.

A still further object of my invention is to provi-de a radio receiver which may be tuned exactly to an incoming signal without the aid of sight or hearing, and without preselecting the stations.

A still further object of my invention is to provide an improved magnetic clutch which may be utilized in my improved tuning apparatus.

In one embodiment of my invention, I couple the tuning knob or tuning control of a radioreceiver to the rotor shaft of the tuning condensers through a clutch which preferably is magnetically operated. When tuning between stations, the clutch is energized whereby the capacity of the tuning .condensers can be varied by rotating the tuning knob. The instant that the receiver is tuned to an incoming signal, the amplified signal energy operates a relay tube which de-energizes the clutch, thus disconnecting the tuning knob from the condenser shaft. Consequently, the tuning condensers stop exactly at the point where the receiver is tune-d exactly to the incoming signal, and further accidental rotation of the tuning knob has no effect.

The clutch may be again energized and the receiver tuned to another station either by pushing in the tuning knob, in one embodiment of the invention, or by rotating the tuning knob a predetermined amount, in accordance with another embodiment of my invention.

Other objects, features and advantages of my invention will appear from the following de- (Cl. Z50-20) scription taken in connection with the accompanying drawings in which Figure 1 is a circuit and schematic diagram of a radio receiver embodying my invention;

Fig. la is a set of curves showing certain characteristics of the circuit illustrated in Fig. 1

Fig. 2 is a schematic diagram of another embodiment of my invention;

Fig. 3 is a view taken on the line 3 3 of Figure 2; and

Fig. 4 is an exploded View of a portion of the structure shown in Figs. 2 and 3.

Referring to Fig. l, one embodiment of my invention is shown applied to a superheterodyne receiver. The receiver includes a radio frequency amplifier I having an input circuit which is coupled to an antenna 3 through a transformer 5, and having an output circuit coupled to a first detector 'I through a transformer 9.

The secondary windings of the transformers 5 and 9 have variable tuning condensers II and I3, respectively, connected thereacross in the usual manner, for selecting a desired incoming radio signal. An oscillator I5 is provided which is coupled to the first detector 'I for the purpose of heterodyning an incoming signal to produce an intermediate frequency signal in the output circuit of the first detector.

The frequency of the oscillator output may be varied by adjusting a variable condenser I'I which preferably, is one unit of a gang condenser including the tuning condensers II and I3, these three condensers being variable through a common control device as indicated by the dotted line I9.

The output of the rst detector 'I is transferred to the input circuit of an intermediate frequency amplifier 2I through a tuned intermediate frequency transformer 23. The output of the intermediate frequency amplier ZI is likewise transferred to the input circuit of the second detector 25 through a tuned intermediate frequency transformer 2, the second detector being a diode rectier which is one unit of a diode-triode vacuum tube 29.

The tuned transformers 23 and 21 are bandpass filters which have a pass range of sufficient width to pass the intermediate frequency carrier and at least one signal side band.

The circuit of the second detector includes a resistor 3| across which the audio signal appears. This signal is impressed upon the control grid of an audio frequency amplifier tube 33 through a conductor 35.

The resistor 3I is shunted by an intermediate 55 frequency bypass condenser 31, whereby the intermediate frequency voltage output of amplifier 2| is impressed across the second detector or diode rectifier elements 39 and 4| through a low impedance circuit. Y

In the preferred embodiment of the invention, both automatic volume control and noise suppressor circuits are included, which are utilized for increasing the selectivity of the receiver in addition t0 performing their usual functions. The automatic volume control may be obtained by connecting the control grids of the amplifiers and 2| 'and the first detector 1 to the negative or plate end of the resistor 3| through resistors 43, 45, and 41 individual to the control grids and through a common filter resistor 49.

A filter condenser 5| is connected between the grid end of the resistor 49 and ground, for preventing audio frequency or higher frequency voltage variations from being impressed upon the control grids. Any increase in the strength of the carrier wave of a received signal will increase .the voltage dr'op across the resistor 3| whereby the control grids of tubes 1, and 2| will become more negative to lower the gain in the tubes.

The noise suppressor circuit includes an intermediate frequency amplier tube 53, a diode rectifier 55, and a control tube 51. The input circuit of the intermediate frequency amplifier tube Y53 is coupled to the output circuit of the tuned intermediate frequency transformer 23 through a coupling condenser 59 and a coupling resistor 6|.

Upon reception of a signal, the intermediate frequency output of the amplifier tube 53 is trans ferred to the diode rectifier 55 through a transformer 63 sharply tuned to the intermediate frequency, whereby a voltage drop is produced along a resistor 65 in the diode rectifier circuit.

The cathodes v69 and 61 of the diode rectifier `55 and the control tube 51, respectively, are connected together through a conductor 1|, whereby -both cathodes are connected to one end ci the resistor 65. The control grid 13 of the control tube 51 is connected to the other end of the resistor 65, whereby the control grid, 13, will be made highly negative with respect to its cathode when current flows in the resistor 65.

The plate 15 of the control tube 51 is supplied With positive potential from any suitable source, such as a battery 11. The negative terminal of the battery is connected to ground so that the plate circuit of the control tube 51 includes the biasing resistor 19 of the intermediate frequency amplifier 2|.

When there is no incoming signal, there is no voltage drop along the resistor 65 of the diode rectifier 55, and the grid 13 of the control tube 51 is at the same potential as its cathode 61. Therefore, with no incoming signal, a current flow is maintained through the plate circuit of the control tube 51 which produces a voltage drop in the biasing resistor 19 of the intermediate frequency amplifier 2| sufficient to make amplifier 2| ineffective.

As soon as the variable condensers |3, and |1 are tuned to the frequency of an incoming signal, the resulting current iiow in the resistor 65 biases the control tube 51 to cut-off, and the noise suppressor current no longer flows through the biasing resistor 19 of amplifier 2|. Thus, upon reception of the signal, the receiver becomes operative to supply a signal to the loudspeaker,

In accordance with a specific embodiment of my invention, the tuning knob 8| of the radio aocaees receiver is coupled to the rotor Shaft of the condensers I3, and, |1 through a magnetic clutch which comprises a U shaped iron core 81 having a magnet coil 89 wound thereon. Two clutch plates 9| and 93 are provided, the plate 9| being fastened to one end of a shaft 95 rotatably mounted in one leg of the iron core. This shaft is connected to the rotor shaft 0f the gang condenser, as indicated by the dotted line I9.

The other clutch plate 93 is fastened to one end of another shaft 91 which is rotatably mounted in the other leg of the iron core. Y

The tuning knob 8| is provided with a sleeve 99 and is mounted upon one end of the shaft 91 in such a manner that it is axially movable with respect to the shaft, but not rotatably movable with respect thereto.

A flange |0| is provided on the tuning knob sleeve 99 for cooperation with a switch |03. The switch |03 may be closed by pushing the tuning knob 8| in towards the panel indicated at |05, while the clutch shaft 91 may be rotated by the tuning knob when it is in any axial position.

The clutch plates 9| and 93 may comprise flexible saucer-shaped discs of soft iron which are mounted so close together that when current iiows through the magnet coil 89, they are pulled together by the magnetic flux passing through the iron core 81 and through the shafts 95 and 91, these shafts being made of magnetic material.

It will be apparent that when the magnetic coil 89 is energized, the radio receiver may be tuned by rotating the tuning knob 8|, and that when the magnetic coil 39 is de-energized, the setting of the tuning condensers I3, and |1 cannot Vbe changed by rotation of the tuning knob.

Referring now to the control circuit for the magnetic coil 89, the triode portion of the diodetriode Vacuum tube 29 functions as a control tube for the clutch 85. The control grid |01 of the tube 29 is connected to the negative end of the diode resistor 3| through a filter resistor |09.

The grid end of the filter resistor |09 has an alternating current connection toV ground through a filter condenser The filter, consisting of the resistor |09 and condenser is provided for the purpose of preventing alternating voltage f uctuations from being impressed upon the control grid |01.

The plate 3 of the vacuum tube 29 is supplied with positive potential from a suitable source such as a battery ||5 having its negative f terminal connected to ground and its positive terminal connected to one end of the magnet coil 89. The other end of the magnet coil is connected to the plate 3 through a conductor It will be evident that when the receiver is not tuned to an incoming signal, there will be no Voltage drop along the diode resistor 3|, and the control grid |01 of the triode section will be at ground potential. Therefore, there will be a flow of current in the plate circuit of the triode section, this current flowing through the magnet coil 89 and energizing the clutch 85. Consequently, so long as no signal is being received, the receiver may be tuned by rotating the tuning knob 8|.

As soon as the receiver is tuned to an incoming signal a voltage drop appears across the diode resistor 3|, and the grid |01 is made sufiiciently negative to block the tube, -whereby the ,7,5

magnetic clutch 85 is cle-energized.- As a result, the tuning condensers |I, I3, and I1 are disengaged from the tuning knob 8| so that they stop exactly at the point where the station is tuned in, and further accidental rotation of the tuning knob does not detune the receiver.

It may be noted that the use of a sharply tuned circuit is important in obtaining proper operation of the clutch. This will be more readily understood by referring to Fig. la where curve |20 is the resonance or selectivity curve of the noise suppressor, and brake circuit (determined primarily by tuned transformer 63), while curve I 22 is the selectivity curve for the signal channel (determined primarily by tuned transformers 23 and 21). By making the brake circuit much more sharply tuned than the signal channel, the brake is prevented from operating before the receiver is tuned to the carrier frequency itself, that is, to the middle of the communication channel. f

It will be understood that the rotors of the tuning condensers should be properly counterbalanced or provided with sufficient friction to hold them in any position in which they are stopped.

When it is desired to tune away from a station, the tuning knob 8| is again connected to the tuning condensers through the clutch 85 by pushing in on the tuning knob to close the switch |03. This causes current to iiow from the battery II5 through the magnet coil 89, the resistor IIS, and the switch |03 so that the clutch is energized.

After the tuning knob has been pushed in and rotated far enough to tune out the station that was being received, the tuning knob is permitted to spring out away from the panel, whereby the switch I 03 is opened and the receiver is incondition to stop automatically on the next station. The tuning knob is then rotated further until the receiver is tuned to the next station at which time the clutch is again automatically de-energized to stop the condensers at the correct position.

If it is desired to tune the receiver in the conventional manner, a switch |2| may be closed which causes the clutch 55 to remain energized at all times.

Referring to Fig. 2, there is shown a diierent mechanism for energizing the clutch when it is desired to tune away from a particular station. This mechanism is illustrated in connection with the same rectifier circuit shown in Fig. 1, the receiver being indicated schematically at |25. In the two figures, like parts are indicated by the same reference numerals.

In Fig. 2 the tuning knob 8| is shown rigidly connected to the clutch shaft 91. By means of a mechanism indicated generally at |21, the clutch may be energized by rotating the tuning knob 8| through a predetermined number of degrees.

Referring to Figs. 2, 3, and 4, the mechanism for obtaining this control comprises an arm |29 pivotally mounted at one end and connected at the other end to the iron core I3I of a solenoid |33. The arm |29 is provided with supporting members |32 in which a shaft |35 is mounted. A gear wheel |31 is rotatably mounted upon the shaft and is positioned above a gear Wheel |39 keyed to the clutch shaft 91.

A contact disc MI, having diametrically opposed contact pins |43 and |45, is rotatably mounted upon the shaft |55 for the purpose of actuating a clutch energizing switch` |41. The position of the contact disc Ifll may be controlled through the gear wheel |31 by means of two spiral springs |49 and I5I.

The inner end of the spring |49 is mechanically connected to the gear wheel |91 through an arm |53, as indicated by the dotted line |55 in Fig. 4. The outer end of spring |49 is connected to the Contact disc MI through an arm I 51,as indicated by the dotted line I 59 (Fig. 4) whereby rotation of the gear wheel |31 will rotate the contact disc.`

There is also a connection between the contact disc I4! and the outer end of the spring I 5| through an arm 33|, the inner end of this spring being fastened to the supporting members |32 through an arm it, these connections being indicated by the dotted lines |55 and |51, respectively, in Fig. 4. Since one end of the spring |5I is fastened to a xed point, it opposes the rotation of disc IM. If the springs H59 and I5! are identical, as they preferably are, a half rota,- tion of the gear wheel |31 in either direction causes a quarter` rotation of the disc IiiI. Assuming the gears I 31 and i 39 have a one to one ratio, a. half rotation of the tuning knob 8| likewise causes a quarter rotation of disc |4I.

The magnet coil |59 of the solenoid |33 is connected in series with the magnet coil 89 of the clutch 85 so that when theclutch 85 is energized by plate current from the vacuum tube 29 the solenoid |33 is energized and the gear wheel |31 is pulled up out of contact with the lower gear wheel |39. It will be noted that at any time the receiver is not tuned in to an incoming signal, the clutch 85 will be energized and the two gear wheels will be held out` of engagement.

As soon as the receiver is tuned to an incoming signal by rotating the tuning knob 8| the vacuum tube 29 is blocked by the incoming signal and the clutch 85 is instantly de-energized to disconnect the tuning knob from the tuning condenser shaft, as described in connection with Fig. l. In addition, the solenoid |33 is de-energized and the gear wheel |31 immediately drops into engagement with the lower gear wheel |39.

From the foregoing description of the contact disc mechanism, it will be apparent that, if the operator turns the tuning knob 8| a slight amount after the clutch is de-energized, there will be no change in the circuit conditions and the receiver will remain tuned in on the station just received.

If the operator desires to tune away from this particular station and tune in the next station, the tuning knob 8| is rotated a predetermined amount, a half turn, in the embodiment illustrated, with the result that the contact disc is rotated suiiiciently to force either the contact pin I t3 or the pin |45 against a switch arm |1I and close the switch |41.

Current then flows from the battery IIE, through the switch |41, and the resistor I|9, and the clutch 85 is instantly energized. A further rotation of the tuning knob 3| rotates the tuning condensers II, I3, and I1 and the receiver is tuned away from the station that was being received. This results in the blocking potential being removed from the grid of the vacuum tube 29, the clutch 85 is energized by the plate current of the tube 29 and, at the same time, the solenoid |33 is energized to pull the gear wheel |31 out of engagement with the lower gear wheel |29.

As soon as the gear Wheels are moved out of engagement, the springs |449 and |5| cause the gear wheel |31 and the contact disc |4| to rotate back to their original positions and the switch |41 is opened. The circuit is now back to its original condition, and as soon as the tuning knob is further rotated to a point where the receiver is tuned to the next station, the clutch and solenoid windings 89 and |69 are again automatically de-energized.

Ity should be understood that the above-described mechanism may be adjusted to cause engagement of the clutch vin response to any desired degree of rotation of the tuning knob. Such an adjustment may be made either by changing the gear ratio of the gears |31 and |39, or by changing the positions of the contact pins |43 and |45.

It should also be understood that a reducing gear or some other slow-motion drive (not shown) is employed for coupling the clutch shaft 95 to the tuning condensers |3, and Thus, a half turn of the tuning knob will cause only a slight rotation of the tuning condensers.

`From the foregoing description, it will be seen that I have provided what may be referred to as an automatic tuning system which greatly increases the ease with which any radio receiver may be tuned and which makes it practical to increase the selectivity of radio receivers to a degree that would make them exceedingly diicult to operate with a conventional tuning control.

While I have described only two embodiments of my invention it will be apparent that various other modifications may be madey therein without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1. A radio receiver comprising a tunable circuit for selecting a carrier wave, said tunable circuit including a variable tuning unit, a manual tuning Control device, a clutch for mechanically coupling said tuning unit and said tuning device, and means for disengaging said clutch in response to the selection and reception of a Carrier wave by said tunable circuit.

2. A radio receiver comprising a tunablev circuit for selecting a carrier wave, said tunable circuit including a variable tuning unit, a manual tuning control device, an electromagnetic clutch normally energized for mechanically coupling said tuning unit and said tuning device, and means for deenergizing and permitting disengagement of said clutch in response to the selection and reception of a carrier wave by said tunable circuit.

3. A radio receiver comprising a tunable circuit for selecting a carrier Wave, said tunable circuit including a variable tuning unit, a manual tuning control device, a clutch connecting said tuning unit and control device and being electrically operable, a control tube having an anode circuit energized to cause said clutch normally to engage, and means for applying to said control tube a biasing potential proportional to the strength of a selected and received carrier wave for substantially deenergizing said anode circuit, thereby to release said clutch.

4. A radio receiver according to claim 1 characterized in that said tuning device is a manually operable tuning knob, and further characterized in that means is provided for selectively engaging said clutch by moving said tuning knob to a predetermined position after said clutch has been disengaged.

5. .A radio receiver according to claim 1 characterized in that said tuning device is a manually operable tuning knob, and further characterized in that means is provided for selectively engaging said clutch by moving said knob axially after said clutch has been disengaged.

6. A radio receiver according to claim l char:

acterized in that said tuning device is a manually operable tuning knob, and further characterized in that means is provided for selectively engaging said clutch by rotating saidknob a predetermined number of degrees after said clutch has been disengaged.

` 7. In a radio receiver of the superheterodyne type, means for converting an incoming radio signal to an intermediate frequency signal having a predetermined frequency, said means including a variable tuning element, a clutch through which said element may be Varied, a magnet coil for said clutch, a relay tube having an output circuit, said output circuit being connected to said magnet coil, whereby said clutch is engaged when said relay tube is energized, and means including a circuit tuned to said intermediate frequency for de-energizing said relay tube in response to the reception of an incoming signal, whereby said clutch is disengaged.

8. A radio receiver comprising a tunable circuit for selecting a radio signal, said circuit including a variable tuning unit, a manually operable tuning knob, a clutch for mechanically coupling said tuning unit and said tuning knob, means for disengaging said clutch in response to the selection of a radio signal by said tunable circuit, and means including a switch for selectively engaging said clutch, said last means including a rotatable elementJ positioned to operate said switch when rotated a predetermined amount and a driving unit for mechanically coupling said rotatable element to said tuning knob whereby said rotatable element may be rotated by turning said tuning knob, and means for uncoupling said rotatable element and said tuning knob in response to the Selection of a radio signal by said tunable circuit.

9. A radio receiver comprising a tunable circuit for selecting a radio signal, said circuit including a variable tuning unit, a manually operated tuning knob, a clutch for mechanically coupling said tuning unit and said tuning knob, means for disengaging said clutch in response tothe selection of a radio signal by said tunable circuit, means for engaging said clutch in response to the closing of a switch, a rotatable element positioned to close said switch when rotated a predetermined amount in either direction, means for mechanically coupling said rotatable element and said tuning knob, means for uncoupling said rotatable element and said tuning knob in response to the selection of a radio signal by said tunable circuit, and means for returning said rotatable element to its original position when said rotatable element and said tuning knob are uncoupled.

RENE A. BRADEN. 

